In a variety of circumstances, it is desirable to control the sonic quality of a region or volume. Such a region or volume includes: an auditorium, movie theater or concert hall; an outdoor stage (whether or not located under a pavilion), an amphitheater; an indoor sports arena with audience seating, an at least semi-enclosed stadium or gymnasium; a room being used as a home theater; an office; and a recording studio.
The existing sound-absorbing panel technology, for example, the Saylor patent (U.S. Pat. No. 4,084,367 to Saylor et al., patented Apr. 18, 1978, is not appropriate for the circumstances mentioned above. The Saylor patent is directed toward a room partition, i.e., a sound-absorbing free-standing panel, that is sufficiently strong to permit fixtures and accessories to be hung from it. The panels of the Saylor patent are formed of a rigid metal frame to which front and back sheet metal skins are attached. The cavity defined by the frame and skins is filled with a honeycomb of cells. Holes are selectively punched into the skins to convert the corresponding cells into Helmholtz resonators. Each of the skins is covered by a layer of porous, low density, sound-absorbing material.
The porous, low density, sound-absorbing layers absorb sound in the range of 1000 to 2000 Hertz (Hz). As is well known, a Helmholtz resonator absorbs sound waves of a certain frequency. The Helmholtz resonators of the Saylor patent are tuned to absorb at a frequency of about 500 Hz.
By structurally connecting the core and the frame together, the skins can effectively function as stressed skins. This provides the free-standing panel with substantially increased rigidity, strength and durability. Such a free-standing panel is sufficiently strong to permit fixtures such a desks, bookshelves, file cabinets, etc. to be hung on it.
The Saylor patent acknowledges that there are other ways to construct an acoustic panel, such as a rectangular frame, surrounding around a fiberglass core, covered with fabric. However, the Saylor patent indicates that such a core lacks structural strength, which prevent this type of panel from being sufficiently rigid and strong to permit fixtures such as desks, bookshelves, file cabinets, etc., to be hung from it.
The great rigidity and strength of the panel according to the Saylor patent comes at the expense of great weight. This is not a significant problem for the intended purpose of the Saylor patent, namely a free-standing room partition. However, as recognized above, there are a great many circumstances in which an acoustically significant panel need not be free-standing, nor can it be very heavy.
For example, in a recording studio, it is desirable to control the acoustics of the room by attaching acoustically significant panels to the walls and/or ceiling. This is impractical with very heavy panels. Similarly, in a pavilion, arena or gymnasium, it is impractical to attach a great many very heavy panels to a ceiling that spans a great distance. Unless specifically engineered to handle such a load (at a much greater construction cost), a roof/ceiling of a pavilion, arena or gymnasium cannot support a great many, very heavy panels such as those of the Saylor patent.
The metal skins of the acoustic panel according to the Saylor patent also act as diffusers of sonic energy, which undermine the effectiveness of the overall sound-absorbing ability of the free-standing panel. This is recognized in the Fearon patent (U.S. Pat. No. 4,522,284 to Fearon et al., patented Jun. 11, 1985), which indicates that the skins reflect a large percentage of sound back into the work area. The Fearon patent departs completely from the stressed skin technique of the Saylor patent. Instead, the Fearon patent discloses a composite acoustic panel that is a sandwich of a layer of molding media, a honeycomb of cells and another layer of molding media. Despite the Saylor patent's extensive discussion of Helmholtz resonators formed in the stressed metal skins, the Fearon patent does not contemplate forming Helmholtz resonators in the core of the "molding media sandwich."